Breeding loan are done the female will typically move to the male to which she should be bred too (this is to avoid sending a male and the male being bred to every female possible without it being disclosed)
The first thing is to have a solid contract that covers anything from QT to vet care if necessary to split to first choice (not all slipt are 50/50 it depends on the value of the animal being paired)
It's a tricky process sometime the animal does not go that season and has to stay another season.
The problem is many people have been burned, things did not happen the way they should (typical when money is involved), honestly it's best to save up and by the animal you need then go through that headache.
I have done loans with some dear friends but we value our friendship more than any monetary outcomes and many of the loans I did was to help others and did not even keep any animals.
Again risky tricky I have seen friendship ruined over this.